The yeast Genetic Stock Center has been in operation since the early 1960's and has been officially funded by the NSF since 1972. The YGSC maintains and disseminates strains of S. cerevisiae for use in basic and applied research in the biological sciences and for teaching purposes. The collection contains about 850 genetically well-characterized strains, which are periodically checked for markers and ploidy. Improved versions of particular strains are occassionally constructed by the YGSC, preserving as much as possible of the original genome. Completely now constructs (such as opposite mating type or limited additional auxotrophies) for certain mutants are periodically made and added to the collection. Well characterized new strains of general interest and usefulness are solicited from, or deposited by, various investigators, and, once checked, are incorporated into the collection. At intervals of 2 of 3 years, the YGSC publishes and distributes to more than 1000 investigators and educators a catalogue listing all strains in the collection, their genotypes, sources and pertinent references. Approximately 100 strains are requested and supplied each year. This year, requests have already exceeded 1000 strains. New techniques have recently been adapted for use in better characterizing strains in the collection. Orthogonal Field Alteration Gel Electrophoresis (OFAGE), in conjunction with DNA-DNA hybridization, is being implemented by the YGSC for the karyotyping of various "key" strains of S. cerevisiae and other yeast genera, as well as for the identification of chromosomal anomalies (translocations, rearrangements and other ploidy phenomena) in certain strains in the collection.